Reverse Engineering for Beginners

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CHAPTER 6.PRINTF()WITH SEVERAL ARGUMENTS CHAPTER 6.PRINTF()WITH SEVERAL ARGUMENTS


.text:0000000C sw $ra, 0x38+var_4($sp)
.text:00000010 sw $gp, 0x38+var_10($sp)
; pass 5th argument in stack:
.text:00000014 li $v0, 4
.text:00000018 sw $v0, 0x38+var_28($sp)
; pass 6th argument in stack:
.text:0000001C li $v0, 5
.text:00000020 sw $v0, 0x38+var_24($sp)
; pass 7th argument in stack:
.text:00000024 li $v0, 6
.text:00000028 sw $v0, 0x38+var_20($sp)
; pass 8th argument in stack:
.text:0000002C li $v0, 7
.text:00000030 lw $t9, (printf & 0xFFFF)($gp)
.text:00000034 sw $v0, 0x38+var_1C($sp)
; prepare 1st argument in $a0:
.text:00000038 lui $a0, ($LC0 >> 16) # "a=%d; b=%d; c=%d; d=%d; e=%d; f=%d⤦
Ç; g=%"...
; pass 9th argument in stack:
.text:0000003C li $v0, 8
.text:00000040 sw $v0, 0x38+var_18($sp)
; pass 1st argument in $a1:
.text:00000044 la $a0, ($LC0 & 0xFFFF) # "a=%d; b=%d; c=%d; d=%d; e=%d; f⤦
Ç=%d; g=%"...
; pass 2nd argument in $a1:
.text:00000048 li $a1, 1
; pass 3rd argument in $a2:
.text:0000004C li $a2, 2
; call printf():
.text:00000050 jalr $t9
; pass 4th argument in $a3 (branch delay slot):
.text:00000054 li $a3, 3
; function epilogue:
.text:00000058 lw $ra, 0x38+var_4($sp)
; set return value to 0:
.text:0000005C move $v0, $zero
; return
.text:00000060 jr $ra
.text:00000064 addiu $sp, 0x38 ; branch delay slot


Non-optimizing GCC 4.4.5


Non-optimizing GCC is more verbose:


Listing 6.18: Non-optimizing GCC 4.4.5 (assembly output)

$LC0:
.ascii "a=%d; b=%d; c=%d; d=%d; e=%d; f=%d; g=%d; h=%d\012\000"
main:
; function prologue:
addiu $sp,$sp,-56
sw $31,52($sp)
sw $fp,48($sp)
move $fp,$sp
lui $28,%hi(gnu_local_gp)
addiu $28,$28,%lo(
gnu_local_gp)
lui $2,%hi($LC0)
addiu $2,$2,%lo($LC0)
; pass 5th argument in stack:
li $3,4 # 0x4
sw $3,16($sp)
; pass 6th argument in stack:
li $3,5 # 0x5
sw $3,20($sp)
; pass 7th argument in stack:
li $3,6 # 0x6
sw $3,24($sp)
; pass 8th argument in stack:
li $3,7 # 0x7

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